An insulated gate bipolar transistor (hereinafter, referred to as IGBT) is generally used as a power semiconductor device having a breakdown voltage of not less than 600 V.
Since the power semiconductor device is generally used as a switch, it is desired that the power semiconductor device has a low ON resistance and a high switching speed. In order to reduce the ON resistance, a trench gate structure which extends further deeply into an n−-type base layer from a channel region is used. The structure enables carriers to be effectively confined in the n−-type base layer between the adjacent trench gates in order to cause conductivity modulation, and accordingly, the ON resistance of the IGBT is reduced.
However, due to the trench gate structure deeper than the channel, delay in the carrier storage at the period of transfer (turn-on) of the IGBT from the OFF state to the ON state is large, and delay in the carrier discharge at the period of transfer (turn-off) of the IGBT from the ON state to the OFF state is large. Accordingly, there is a problem that a switching loss at the period of turn-on and a switching loss at the period of turn-off are large.